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356

Girders and Ships.

Prepare the longitudinal stays and manhole seating; put in place,
with fittings; and test the boiler as before.

The Vertical and Water-tube Boilers present no further diffi-
culty. Taking the first, the shell is built-up separate from the
firebox and chamber. Machine riveting can be used for most of
this work " But when putting together, the foundation ring is the
only other part that can be done by machine; all the rest is hand
work. The tubes are expanded into the tube plates as before.

The Water-tube Boiler (f. 338) has its tubes cut to length,
and expanded into the headers; the chambers a b flanged and
welded; while the making of G will be understood from previous
descriptions.

As further examples of Plate Work, we illustrate a Girder at
Fig. 318 and a Roof Principal at Fig. 319; but these are'simple
in comparison with boilers, as far as their practical construction
is concerned. The Box Girder has its plates and angles sheared
to dimension, the holes then marked off, punched, and rimered
in position. The angles A and web plates B are first riveted,
and next connected to the booms c c: so it will be clear that no
hand-riveting whatever is necessary. The Roof Principal needs
no explanation. The first application of portable riveting to
bridge erection was made by Mr. Tweddell in 1873, on tne
Primrose Street Bridge, London.

Ships are now built of steel plates and angles, whose dimen-
sions are carefully got out by the draughtsman in the first place.
Much more drilling is now done than formerly, though a con-
siderable amount of punching prevails, and the plates are usually
sheared. The keel and framing are first erected, and the plates
then adjusted and marked from these. As regards the riveting
up, nothing could shew this better than the diagram at Fig. 301.
Of course there are many plates too long to be reached by the
machine, but this diagram shews what an extraordinary amount
of worf can be performed by these wonderful * Portable Riveters/